There are many situations in which integrated circuits mounted on a circuit board need to be tested or monitored in real-time. In such situations, there is no substitute for directly probing an integrated circuit on a circuit board. Such real-time testing is particularly important with complicated integrated circuit chips, like microprocessors, because circuit characterization and debugging is otherwise much more difficult.
As integrated circuits become more complicated, the testing of the integrated circuits becomes more difficult. Integrated circuits often have several hundred connector pins. Hence, although difficult, a probing apparatus must provide reliable electrical contact with each pin in a non-destructive way.
Conventionally, when it is necessary to probe a large-pin count integrated circuit, such as a pin-grid array (PGA), for testing, the circuit board having the integrated circuit mounted thereon is outfitted with a socket (as referred to as a base socket). The socket is directly soldered to the circuit board. When the integrated circuit is not being tested or monitored, the integrated circuit is plugged into the base socket. However, when the integrated circuit is to be tested or monitored, a break-out adapter is plugged into the socket, and the integrated circuit is plugged into the break-out adapter. In effect, the break-out adapter is another socket between the base socket attached to the circuit board and the integrated circuit.
The break-out adapter functions to fan-out signals from each of the pins on the integrated circuit to various stakes positioned on the break-out adapter. Then, typically users would interconnect a logic analyzer to the pins of the integrated circuit by connecting individually terminated test probe leads between the logic analyzer and the stakes. Alternatively, groups of the probe leads would be connected to a common multi-wire ribbon connector which in turn connects to the logic analyzer.
There are several difficulties associated with the conventional approach to probing integrated circuits for testing, particularly those integrated circuits with larger pin counts. The use of a break-out adapter is problematic because the physical size or area of the break-out adapter is typically five to six times the area of the integrated circuit and thus covers the base socket so as to make it difficult or impossible to actuate zero insertion force mechanisms used with many base sockets. As a result, the interconnections between the break-out adapter and the base socket are mechanically unstable and electrically unreliable.
Another difficulty with the conventional probing approach is that integrated circuits cannot be probed without powering down the integrated circuit or the circuit board having the integrated circuit mounted thereon. For example, to attach a break-out adapter the circuit board must be powered down because it requires that the integrated circuit first be removed from the base socket, the break-out adapter be installed into the base socket, and then the integrated circuit be plugged into the break-out adapter. The problem with the conventional probing approach is that the particular state of the integrated circuit which initiated the need to probe the integrated circuit (e.g., device characterization or debug) is lost when powered down. In many cases it is difficult and time consuming to recreate the state of the integrated circuit which initiated the need to probe the integrated circuit. The required power down and later power up are themselves also time consuming.
Additional difficulties of the convention approach are that sockets are required and break-out adapters do not provide decoupling terminations. The conventional approach requires that base sockets for receiving the integrated circuit be soldered to the circuit board. The sockets not only add to the weight and total cost of the circuit board but also reduce reliability. Also, the lack of decoupling terminators with break-out adapters requires that individual probe leads must be used to connect to the break-out adapter and that these leads must be individually terminated. As a result, with large pin-count integrated circuits, such connections require a large amount of time and result in heavy, bulky and cumbersome interconnections to the break-out adapter.